It is known that many fuel assemblies for power reactors, and particularly for light water reactors, comprise a skeleton constituted by a rigid structure formed by a bundle of guide tubes joining two end pieces and on which grids are fixed are regular intervals. These grids support end brace pencils each formed by a stack of pellets of fuel material in a cylindrical sheath. The major portion of the guide tubes are generally distributed in rows arranged along two perpendicular directions. An assembly of this type is described, for example, in French Pat. No. 2,049,108.
The skeleton of a fuel assembly must be so mounted as to avoid the appearance of stresses or of weak points, sources of welding ruptures. The fixing of the inner guide tubes to the grids is moreover very inconvenient, due to the difficulty of access into the bundle. In the past, the guide tubes were fixed to the grids by welding when the constituent materials of the guide tubes and of the plates constituting the grids were compatible. However the manual forming of welds on four longitudinal lines of each guide tube in contact with the plates represents very long, troublesome operation of uncertain reliability, due to the difficulties of correctly positioning the welding tool.